Various fixes related to the C++11/14 update (see issue #3140)

- Convert scoped_ptr to std::unique_ptr from <memory>
- Convert arraysize to base::size from include/base/cef_cxx17_backports.h
- Convert NULL to nullptr
- Include include/base/cef_callback.h instead of include/base/cef_bind.h
- Implicit conversion of CefRefPtr<T> or scoped_refptr<T> to T* is gone;
  use .get() instead

See the issue for additional details.

tests/cefclient/browser/main_message_loop_multithreaded_gtk.cc

@@ -7,7 +7,7 @@
 #include <X11/Xlib.h>
 #include <gtk/gtk.h>
 
-#include "include/base/cef_bind.h"
+#include "include/base/cef_callback.h"
 #include "include/base/cef_logging.h"
 #include "include/wrapper/cef_closure_task.h"